Just because you haven't come across it, doesn't mean it is wrong.

Konungedømæ is the older form of Kongeriket, it is actually a form of Old Norwegian- still being used in the early Middle Ages, it is in fact the word Kongeriket that has been borrowed from Danish into Norwegian during the late Middle Ages, possibly under the period of the Kalmar Union. So although both words are correct, I felt it was useful to highlight the older and predominantly Norwegian name for Norway. Norvegr was not an option I'd considered due to it being a reconstructionist name, Noreg however is probably better since it does follow the more likely etymology of Norge stemming from Nor Rig rather than Nor Veg. As you say the Norway and Norge hasn't been proven to come form the same source. It has been argued by some Nordic scholars that Norge's name for itself is unlikely to have been the 'road north' when they lived there, although for the English it would make more sense. Kongariki is Old Norse so I felt that was too far out.
Being a citizen of Scandinavia, an academic author on early Scandinavian history and a languages student, I felt pretty sure I was on the right track.